The present invention relates to a virtual studio and in particular to a position sensing system for such a studio.
In virtual studio systems a chroma-key background is provided in front of which an actor stands. In the TV picture seen by the viewer the chroma-key background is replaced by a virtual scene. Such a system is described in PCT Patent Application No. WO95/30312 to the present applicant.
In the above known system the position of the camera is calculable by using a coded pattern on the chroma-key background. This enables the position of the camera, as well as its orientation and the lens zoom, to be continuously calculated and thereby the perspective of the virtual 3D set can be adjusted correctly to suit the camera position.
This works perfectly for cameras which have a fixed focus and zoom or a fixed position but problems can be encountered in situations where the cameraman is free to simultaneously change the camera position and the lens zoom. For example, when the camera""s optical axis is perpendicular (or almost perpendicular) to the patterned wall, the changes in the captured pattern due to zooming of the lens or to changing the distance of the camera from the wall are identical (or almost identical) and the system cannot extract the correct solution from the captured pattern.
In order to overcome this problem in the present invention, the camera is provided with an independent means for indicating the position of the camera which means are used either alone or in conjunction with the coded pattern and the pattern recognition apparatus to ensure correct interpretation of the position of the camera.
The present invention therefore provides a virtual studio positioning system comprising a chroma-key background panel, a television camera situated in a defined front studio area in front of the background panel for imaging a foreground object in front of the background panel, at least one fixed mounted detection unit the fixed detection unit having a field of view to cover the defined front studio area, an emitting device mounted in a fixed relationship with respect to the TV camera or foreground object the fixed detection unit receiving emissions from the emitting device, and producing a detection output signal, processing means for processing the detection output signal of the fixed detection unit to provide at least x and y coordinates for the TV camera or foreground object in relation to a given origin position in the studio area.
This assumes that the emitting device is in a fixed and known height defining its z value. Preferably the chroma-key background panel comprises a coded chroma-key panel and includes further processing means for processing data extracted from the coded chroma-key panel.
The position information derived from the invention is then used, with the information derived from the pattern recognition system to calculate the accurate perspective information for the background.
Preferably the emitting device is an LED, preferably operating in the non visible part of the electromagnetic spectrum. Preferably the fixed detection device is a static camera, also preferably sensitive to the non visible part of the electromagnetic spectrum region. Preferably both LED and camera operate in the near infra-red.
Preferably the LED is not on continuously but is switched on for a defined time period.
In a specific embodiment the LED emission is coded to provide better distinction from background noise and emission of other LED""s.
Preferably the detection device is also gated to receive emissions during a further defined period which is synchronous to the defined time period.
Preferably the defined time period is shorter than the further defined time period and both periods are synchronised to the frame synchronisation of the studio equipment.
Preferably in a specific embodiment the LED is active for a period of approximately 200 xcexcsec and the detection device for a period of 100 xcexcsec. Preferably the fixed mounted detection unit is mounted at a height above the background panel.
In a further embodiment for a case in which the height of the emitting device is not fixed, a second fixed mounted detection unit is provided.
The invention also then provides means for triangulating the positions given by the first and second detection units to determine the x, y and z positions of the studio camera or the foreground object.
The invention also provides a position sensing system for a TV studio, the system comprising an emission device mounted on an object in a defined area, detection means to detect the radiation emitted by the emission device and providing an output signal, processing means for processing the output signal of the detection means to provide an x,y positional map of the object within the defined area provided that the emission device is in a fixed and known height.
Preferably, the emission device emits radiation within the near infra-red.
Preferably the emission device emits non-continuous radiation only in pulses of defined width.
Preferably the detection means is provided with spectral filter means to collect only radiation in the emission spectrum of the emission device and also with temporal filter means to collect radiation only within a defined time period, the time period being synchronised to the pulse output of the emission device.
In a preferred embodiment for a case in which the height of the emitting device is not fixed, a second detection means is provided having a second output signal, the first and second output signals being used to define the position of the object in the x, y and z directions.
In a further preferred embodiment the positioning system for the studio comprises a position sensing system for a TV studio further comprising a defined structure of at least three LED""s positioned in a fixed relationship with respect to the camera to enable calculation of all camera parameters (x,y,z pan, tilt and roll) and further including a zoom-focus sensor attached to the camera, the system enabling the use of uni-color background panel for displaying a virtual background.
In an alternative embodiment the zoom-focus can be provided from a coded chroma-key panel.